Extracting metals and equilibria Study Guide

Displacement reactions are a specific type of chemical change where a more reactive element displaces a less reactive element from a compound. Crucially, these reactions are also classified as redox reactions. Redox is a portmanteau of reduction and oxidation, referring to the transfer of electrons. Oxidation involves the loss of electrons, while reduction involves the gain of electrons. In a displacement reaction, the more reactive metal atom loses electrons to become a positive ion (oxidation), and the less reactive metal ion gains these electrons to become a neutral metal atom (reduction). This simultaneous electron transfer confirms their classification as redox processes. For example, when zinc displaces copper from copper sulfate, zinc atoms lose electrons (oxidise) to form zinc ions, and copper ions gain these electrons (reduce) to form copper atoms.

Ammonia (NH₃) is formed in a chemical reaction between nitrogen (N₂) and hydrogen (H₂) gases. Nitrogen is extracted from the air by fractional distillation, separating it from oxygen and other atmospheric gases. Hydrogen is mainly obtained from natural gas, commonly methane (CH₄), often through a process called steam reforming. In the ammonia synthesis reaction, nitrogen and hydrogen gases combine according to the balanced equation: N₂(g) + 3H₂(g) ↔ 2NH₃(g). The double arrow is significant because it indicates that the reaction is reversible: ammonia can break down to reform nitrogen and hydrogen. Over time, within a closed system, the rates of the forward (formation of ammonia) and reverse (decomposition of ammonia) reactions may become equal. When this occurs, the system is at dynamic equilibrium. At this point, the concentrations of all reactants and products remain constant, even though both reactions continue to occur.